Extinctionism

Extinctionism is the act of causing every possible monster in a game of NetHack to become extinct. In other words, if you kill enough monsters of one species, then that kind of monster cannot be generated anymore. A creature is extinct when 120 of its kind have been born. Once a species has become extinct, there are very few ways to create new monsters of that species. There are exceptions, however, such as puddingdivision, the monster spellsummon nasties, etc.

Because the most common methods of extinctionism rely on monster generation, unique monsters are ignored by some extinctionists. However, unstoning a statue of a monster will increase the monster count for purposes of extinction; as a result, even unique monsters can be extincted in this sense. Also, monsters that leave corpses can be revived with the undead turning spell or a wand of undead turning and re-defeated. Finally, monsters that resist stoning and leave no corpse can usually wear amulets of life saving and can be extincted with enough amulets, though gathering that many amulets in a non-Wizard mode game is a task that borders on impossible.

Juiblex is the only unique monster that resists stoning, leaves no corpse and does not wear amulets (he has no head to hang them on), making him the only monster in the game that can be killed only once. If you summon him by sacrifice, he will not appear in his lair.

Keystone Kops do not become extinct even after 120 of each kind have been created.

The easiest way to play an extinctionist is to play as a wizard. The wizard has the ability to cast create monster with no hunger penalty, and with the Eye of the Aethiopica he can cast virtually indefinitely. There is no reason another class couldn't do extinctionism; it would simply be more challenging.

Once you have the Eye, make sure to gather up all the various resistances, including magic resistance, and reflection. It would be very bad to lose your character to a random gnome with a wand of death. Make sure you have a decent set of armor, and a good weapon as well.

A common method to rack up kills is to build a boulder fort around an altar. Then stand behind the altar and cast create monster over and over, while killing the resulting monsters and sacrificing them to your god.

You can either just summon monsters and kill them at random, or try to control your summoning.

Controlling your summoning can be done by carefully regulating your own experience level, and picking which dungeon level to summon the monsters on. By keeping your experience level low, you force the game to only summon monsters of a particular difficulty or lower. In this way you can wipe out all the lower level monsters, casting and killing until create monster fails. You can then move down a dungeon level or gain an experience level to increase the monster difficulty.

Erinyes become extinct after 3 have been created and Nazgul become extinct after 9 have been created, as would be expected based on their respective sources (although not all authors held the Erinyes to number three).